Stu Schwartz Pervious Palooza
Westminster, MD 4 June 2015
Pervious Concrete: Hydrologic Design and Performance
Keys for success
• The right application
• The right location
• The right design
• The right timing
• The right mix
• The right contractor
• The right owner / operator
Practitioner stream
Designer/LA Subgrade infiltration, Site Design & Layout for Particulate Loading
Installer Off-load time to curing, moisture control, consolidation and hydration
Inspector Material testing & water content, critical timing,
Supplier Mix-Delivery Time, strength-permeability tradeoff, workability, aggregate
General Contractor Subgrade Compaction, Staging & Clogging Demo & Grading
Engineer/Geotech Hydrologic Design & Structural Design, Constructability, Maintenance
Facility Manager Routine inspection & maintenance, Clogging, Winter Maintenance
Specifications
Beyond Hydrologic and Structural design • ACI 522.1-13 – spec (ACI 522R-15)
• Materials – Mix Proportions • Performance (e.g. 400 in/hr) • Constructability Analysis • Testing: ASTM 1688 ASTM 1701 • NRMCA Contractor Certification • Test Panels – acceptance and reference • Maximum Mix (60* min) and Install (20 min) Timing • Weather Extremes: Misting, Moisture & Insulating Blankets • Inspection and Maintenance • Winter Maintenance • ASTM tests - in progress
Undisturbed subsoil
6” pervious concrete
Underdrain
Clean Stone Subgrade
~30% porosity
Undisturbed subsoil
6” pervious concrete
Overdrain
Clean Stone Subgrade
~30% porosity
Hydrologic Design: Freeze Thaw & Drawdown
Overdrain to Minimize Pavement Saturation
Underdrain to Provide Positive Drainage &
Drawdown
Hydrologic Design at Work 1. MTA Park and Ride – 550 parking spaces 1.77 acres pervious concrete
Section Storage (porosity) Pervious Concrete: 8” 1.6” (20%) #57 Stone: 4 inches to drain invert, 1.2” (30%) + 2.4” (30%) above invert
12 inch total. #2 Stone: ≥ 12 inches 3.6” (30%) Sand: 6 inches 1.8” (30%) Storage below invert: 6.6” 24hr-25 year storm: 6.28” 24hr-100 year storm: 8.65”
With subgrade infiltration of 0.5 in/hr section captures and infiltrates the 100 year storm – zero discharge!
Peak wse 1.57 feet
Hydrologic Design at Work
2. PA Pervious Concrete Sidewalk Design Proposed design:
-520 s.f. pavement -5,700 s.f. contributing drainage (run-on) -24 inch subbase -Total DA = 6,220 s.f. -0.5 in/hr exfiltration
Fails Freeze-Thaw: 1.2 inch storm saturates pavement
Contrast with No Run-on: DA = IA 1.5’ subbase fully infiltrates 8.5 inch storm!
3. Pervious Alley Proposed design:
-1,000 s.f. pavers -10,000 s.f. contributing drainage (CN=95) -48 inch subbase - 8-inch underdrain -minimal exfiltration Exfiltration 0.1 in/hr: ECN 93 Exfiltration 0.52 in/hr ECN 86
Urban Soil Complex
Permeable Pavers
8-inchUnderdrain
48-inches Clean #57 Stone Subgrade ~30% porosity
DA:IA = 10:1
Specifications
Beyond Hydrologic and Structural design • ACI 522.1-13 – spec (ACI 522R-15)
• Materials – Mix Proportions • Performance (e.g. 400 in/hr) • Constructability Analysis • Testing: ASTM 1688 ASTM 1701 • NRMCA Contractor Certification • Test Panels – acceptance and reference • Maximum Mix (60* min) and Install (20 min) Timing • Weather Extremes: Misting, Moisture & Insulating Blankets • Inspection and Maintenance • ASTM tests - in progress
Fresh Density ASTM 1688 ±5 lbs
Surface Infiltration ASTM 1701
Standard Test Method for Density and Void Content of Hardened Pervious Concrete:
ASTM 1754
Specifications
Beyond Hydrologic and Structural design • ACI 522.1-13 – spec (ACI 522R-15)
• Materials – Mix Proportions • Performance (e.g. 400 in/hr) • Constructability Analysis • Testing: ASTM 1688 ASTM 1701 • NRMCA Contractor Certification • Test Panels – acceptance and reference • Maximum Mix (60* min) and Install (20 min) Timing • Weather Extremes: Misting, Moisture & Insulating Blankets • Inspection and Maintenance • ASTM tests - in progress
Inspection and maintenance
0 5 10 15 20 25 30 35
0
5
10
0 5 10 15 20 25 30 35
0
5
10
0 5 10 15 20 25 30 35
0
5
10
0 5 10 15 20 25 30 35
0
5
10
After pressure washing Inspection – condition assessment
Tests were given a “Leakage” classification from 1-3, depending on the size of the wetted footprint after the test. Leakage can indicate sealing/poor performance
Class 1 – very little/no leakage. Wetted footprint is no larger than the device used
Class 2 – some leakage. Wetted footprint is slightly larger than the device used
Class 3 – severe leakage. Wetted footprint is significantly larger than the device used
Fast
8-15 sec.
>100 sec
Slow
Baseline Infiltration Map – White Oak Community Center
215 GPS referenced drawdown
tests
Pervious Concrete Clogging and Maintenance Montgomery County’s White Oak Community Center
Long drawdown time with significant leakage
= clogged pavement
Subprime BMPs
• Site Layout • Hydrologic Design • Infiltration testing • Construction without stormwater design! • Craftsmanship • Inspection and Maintenance Plan • Winter maintenance
Align knowledge and practice across project team Rich Opportunities - High Stakes!
Conclusion
Proven Reliable Green Infrastructure Technologies Avoid Sub-Prime BMPs!!!!!! End-to-End Integration of Knowledge & Expertise across the communities of practice Raise our Game – to reliably get the outcomes we want
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